1. Field of the Invention
The invention relates to an apparatus and a method for the physical therapy of an ankle.
2. Information Disclosure
Ankle injuries are a very common problem in almost all types of athletic endeavors. This group of injuries range from the most mild class 1 inversion ankle sprain to the most severe trimalleolar fractures. In all cases there is loss of integrity of the supporting soft tissues, including ligaments, tendons, and muscles. When any of these structures has been disrupted, there is always a degree of disability which is proportional to the severity of the injury. The objective of therapy is to return the patient to normal activity.
After an acute injury, control of pain and swelling are paramount in beginning rehabilitation. As soon as the pain has subsided, range-of-motion exercises are initiated. In these early stages it is important to protect those movements which are painful and encourage those movements that are not. Devices are known for this phase of treatment. Once the full range of motion is achieved with no discomfort, strengthening of the musculature is begun. Since ligaments generally heal through fibrosis and scarring, rehabilitation of the musculo-tendinous structures is crucial to increasing the stability of the joint. Exercises to extend the range of motion against resistance are required, as well as proprioception exercises to "re-educate" the muscles via the muscle spindle fiber mechanisms.
The earliest range-of-motion exercise is usually passive and devices are specially designed to protect the injured structures. The next phase of rehabilitation involves range of motion exercises against resistance. Initially the amount of resistance must be extremely small because the strength of the affected structures is very limited. It is, however, important to use the full range of motion of the joint regardless of the resistance used. As the patient gains strength in the joint, more resistance will be necessary.
Motion in the area commonly referred to as the ankle joint, is in fact the product of two separate and distinct joints which work together. A first type of motion in this area is dorsiflexion and plantarflexion. Dorsiflexion can be defined as motion occurring in the sagittal plane during which the distal aspect or end of the foot moves toward the tibia or the front of the leg. (See FIG. 3) Plantarflexion can be defined as motion occurring in the sagittal plane during which the distal aspect of the foot or toes move away from the front of the leg, commonly called pointing the toes (See FIG. 4)
The other motions commonly associated with the ankle joint do not in fact take place in the ankle joint itself. They are created at the subtalar joint. The subtalar joint is comprised of the inferior surface of the talus, that bone that sits in the ankle mortice, and the superior surface of the calcaneus, or heel bone. Because of the axis of this joint, motion from this joint goes through all of the three planes of the body. The motions are referred to as pronation and supination. Supination consists of plantarflexion, inversion and adduction. (FIG. 5) Pronation consists of dorsiflexion, eversion and abduction. (FIG. 6)
Inversion and eversion are frontal plane motions. Inversion is motion where the sole of the foot tilts so as to face the midline of the body. (FIG. 7) Conversely, eversion is motion where the sole of the foot tilts away from the midline to the body (FIG. 8).
Abduction is transverse plane motion where the end of the foot moves away from the midline of the body whereas adduction is when the end of the foot moves toward the midline of the body.
The amount of dorsi- and plantarflxion at the subtalar joint is very small; dorsi- and plantarflexion are primarily ankle joint motions. Because of the axis of the subtalar joint, most of its motion is in the direction of inversion/adduction and eversion/abduction. In this way, the ankle/subtalar joint combination works to create all of the motions of the ankle region. For the purpose of the ankle rehabilitation device of the invention, the most important range of motion to focus on is inversion and eversion.
The most common type of ankle injury is the "ankle sprain." This happens when the foot contacts the ground in the plantarflexed and inverted position. As this happens those structures on the lateral aspect of the ankle and subtalar joint, whose function it is to prevent excessive motion in this direction, can be damaged to varying degrees. The more severe the injury, the greater degree of damage and disability. Because the ankle joint is more stable anteriorly, little disability will result in the direction of dorsiflexion and plantar flexion. Therefore the most painful motions lost will be inversion and eversion at the subtalar joint. It is these motions which are strengthened by the ankle rehabilitation device of the invention. (FIGS. 9 and 10)
Three general types of exercise have been recognized: isotonic, isometric and isokinetic. Isotonic exercise involves contraction of the muscles against a fixed resistance or load. As a result of the variable length of lever arm formed by the bone structure in the human body, the forces that must be exerted by the muscles vary while the load remains constant. Therefore, the load must be selected to permit movement during the weakest portion of the body motion and the muscles undergo the strongest contractions only during a short portion of the total movement in the body.
Isometric exercise involves the muscular exertion of portions of the body against a load which is stationary and immobile. While this type of exercise permits the maximum contraction of the muscles employed, the body is prevented from any motion.
Isokinetic exercise resolves the problems noted above with isotonic and isometric exercising. In isokinetic exercising, the muscles of the body exert a force against a load or resistance which is moving at essentially a constant velocity and relatively independent of the actual force exerted by the muscles. Therefore, for rehabilitation and exercise of the ankle, a device permitting isokinetic exercises is preferable.
Devices for ankle rehabilitation are found at each end of the spectrum with regard to sophistication, efficacy and cost. At the inexpensive and unsophisticated end are mechanisms like the Theraband.RTM. System. In this system, a series of straps which have varying amounts of resistance are used. A multitude of logistical problems arise that make this system limited: First, it requires extra apparatus to provide stability to the joints above and below the joint the exercise is designed for, i.e. if one is strengthening the ankle, there is no way to intrinsically stabilize the leg. Second, unless one is meticulous about measuring the distance of the affected part from the stationary part, inconsistencies will arise from session to session. Finally, to strengthen the medial musculature, one must be very imaginative in setting up the exercise. The Theraband.RTM. System for the ankle appears to be able to concentrically and eccentrically exercise the lateral aspect of the joint only.
U.S. Pat. No. 2,467,943 (Mikell) discloses an exercise device for correcting weakened or flabby conditions of the lower leg and foot. The device comprises a pair of foot engaging members which are adapted to engage a patient's foot just back of the ball and under the toes, respectively. A pair of springs and a strap passing over the knee of the patient are attached to the foot engaging members such that a patient may exercise muscles in the leg and foot by overcoming the tension of the springs. The exercise resulting from the use of the Mikell device is isotonic. Moreover, because of the application of force at the ball of the foot, the extensor halluces longus and the peroneus longus are strengthened rather than concentrating the effort on the posterior tibial tendon and the peroneus brevis.
U.S. Pat. No. 5,013,037 (Stermer) discloses a physical therapy device for the rehabilitation of a limb. FIG. 6 discloses a modification of the device for exercising the calf muscles of the leg by flexing or stretching the toe and foot. It is similar in principal and operation to the device of Mikell.
U.S. Pat. No. 3,976,057 (Barclay) discloses a flexing apparatus for joint therapy. The apparatus comprises a plurality of straps holding a linkage means (hinge) and connected by a pneumatic cylinder assembly which may provide active displacement or passive resistance. Because of the hinge, motion is possible in one plane only.
U.S. Pat. No. 4,294,238 (Woodford) discloses a device for assisting and relaxing a user's leg muscles after physical activity. The device includes an elastic strap which extends from under the sole of the user's foot upwardly around the heel to the back of the knee. The elastic strap provides a biasing of the user's foot for assisting the leg muscles.
U.S. Pat. No. 4,371,161 (Williams) describes an ankle and foot exercise apparatus in which a structure attached to the lower leg and a structure that encircles the ball of the foot are connected by an elastic member allowing the foot and ankle to be exercised by moving against the resistance provided by the elastic member. As before, the exercise is isotonic and the wrong muscle groups receive the bulk of the exercise Although motion is allowed along any axis, only flexion works against resistance.
U.S. Pat. No. 4,411,422 (Solloway) discloses an aquatic exercise device comprising a series of sections having rearwardly extending inner fins and generally V-shaped fins that extend outwardly. The device is intended for use when the foot is immersed in water and moved through the water as a source of resistance. It provides isokinetic exercise.
U.S. Pat. No. 4,930,767 (Hamm) discloses a therapeutic device for relieving tension or spasms in the lower back of the human body. The device comprises a foot engaging part, a band to be wrapped above the knee and a pair of elastic straps extending therebetween. It is similar to the devices of Mikell and of Stermer in principle and operation.
At the other end of the rehabilitation spectrum are devices such as that disclosed in U.S. Pat. No. 4,452,447 (Lepley and LaCroix) which discloses a floor-mounted ankle exercising device. The device comprises a frame holding a foot plate which is capable of motion in three perpendicular axes. The motion is controlled by a series of hydraulic cylinders which are in turn controlled by a series of hydraulic valves operated by a series of controls mounted on a vertical extension of the frame. The device permits isokinetic exercise but it is large, complex, and expensive.
There is thus a need for a device which isolates and isokinetically exercises the ankle and subtalar joint complex simply and relatively inexpensively.